Drive mechanism

ABSTRACT

AN INTERMITTENT DRIVE MECHANISM FOR USE IN MACHINE TOOLS HAS DRIVING AND DRIVEN MEMBERS COUPLED BY CONSTANT RATIO GEARS. IN ONE RANGE OF RELATIVE POSITIONS OF THE GEARS DRIVE IS NOT TRANSMITTED THROUGH THE GEARS BUT INSTEAD IS TRANSMITTED THROUGH A CAM AND CAM FOLLOWER. THE CAM IS SO SHAPED AS TO CAUSE A GRADUAL DECELERATION OF THE DRIVEN MEMBER TO ZERO FOLLOWED BY   A GRADUAL ACCELERATION UP TO THE SPEED MAINTAINED BY THE CONSTANT RATIO GEARS.

P 1974 J. E. REEVE Re. 27, 994

DRIVE MECHANISM 2 Sheets-Sheet 1 Original Filed Sept. 13, 1971 April 30,1974 REEVE Re. 27, 994

DRIVE MECHANISM 2 Sheets-Sheet z Uriginil] Filed Sept. 13, 1971 UnitedStates Patent Olfice Relissued Apr. 30, 1974 27,994 DRIVE 'MECHANISMJohn Edwin Reeve, London, England, assignor to Thorn ElectricalIndustries Limited, London, England Original No. 3,710,639, dated Jan.16, 1973, Ser. No.

179,823, Sept. 13, 1971. Application for reissue July 17, 1973, Ser. No.379,919 Claims priority, application Great Britain, Sept. 16, 1970,

44,316/70 Int. Cl. F1611 1/16, 27/04, 35/02 US. Cl. 74-393 21 ClaimsMatter enclosed in heavy brackets appears in the original patent butforms no part of this reissue specification; matter printed in italicsindicates the additions made by reissue.

ABSTRACT OF THE DISCLOSURE An intermittent drive mechanism for use inmachine tools has driving and driven members coupled by constant ratiogears. In one range of relative positions of the gears drive is nottransmitted through the gears but instead is transmitted through a camand cam follower. The cam is so shaped as to cause a gradualdeceleration of the driven member to zero followed by a gradualacceleration up to the speed maintained by the constant ratio gears.

BACKGROUND OF THE INVENTION This invention relates to a drive mechanismfor producing intermittent or cyclically variable motion. Such devices,commonly known as indexing mechanisms, are used in machine tools,packaging machines and other special purpose machines for elfecting thetransfer of workpieces, or of a part of the machine, through a number ofpredetermined positions in sequence.

Conventionally a Geneva mechanism or a cam and follower system is usedwhere definite control of the indexing motion is necessary. Suchmechanisms must be large, and therefore costly, when used to index aheavy mass through a large angle, because all the energy required forthis purpose must be transmitted during one revolution or less of thedriving member.

SUMMARY OF THE INVENTION An object of the invention is to provide anindexing mechanism which is of exceedingly simple construction and yetwhich is effective in operation.

The invention consists in a drive mechanism which has a cam and camfollower coupled to respective ones of a driving member and a drivenmember. The cam follower engages with the cam when the members arewithin a range of relative positions to transmit drive from the drivingmember to the driven member, and when the members are not within saidrange drive is effected through constant ratio gears. By appropriatelyshaping the cam, the drive mechanism can be constructed so as to causethe driven member to experience a predetermined acceleration, a constantspeed (drive being through the constant ratio gears) and then apredetermined deceleration.

Preferably the cam is on the driving member and the cam followers are onthe driven member. Conveniently the gears may comprise a first gear onthe driving member and a second gear on the driven member which engageswith the first gear but which has teeth missing corresponding to thesaid ranges of positions where drive is transmitted through the cam andcam follower.

BRIEF DESCRIPTIONS OF THE DRAWINGS Other objects and advantages of theinvention will become apparent from a description of the followingdetailed description taken with reference to the accompanying drawings,in which:

FIG. 1 is a plan view of a first indexing mechanism embodying theinvention;

FIG. 2 is a side view of the mechanism of FIG. l;

FIG. 3 shows an alternative cam for use in the mechanism of FIG. 1;

FIGS. 4, 5 and 7 are plan views of three further indexing mechanismsembodying the invention; and

FIGS. 6 and 8 are views similar to FIG. 2 of the mechanisms of FIGS. 5and 7 respectively.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The mixed motion drivemechanism shown in FIGS. 1 and 2 transmits drive from a driving shaft 10to a driven shaft 12. The driving shaft 10 carries a cylindrical cam 14and a worm or spiral pinion 16, and the driven shaft 12 carries a wormwheel or spiral gear 18 for engagement with the worm or spiral pinion16. As illustrated, two cam follower sets 20 are attached to the wormwheel 18 for engagement with the cam 14. Each set in this contextconsists of two followers.

The cam track 22 of the cam 14 is of varying slope, i.e. at the ends ofthe track drive is transmitted from the cam to the cam follower while atthe center of the track (the position illustrated in FIGS. 1 and 2) nodrive is transmitted. Thus on rotation of the cam 14 from one end of itstravel to the other at constant speed the cam follower set willexperience controlled deceleration to zero speed followed by controlledacceleration.

The speed attained by the driven member when the cam follower set 20reaches the end of the track 22 is maintained by the worm 16 engagingwith the worm wheel 18 as the follower 20 nears the end of the track 22.This constant speed ratio is maintained until the next cam follower set20 engages the cam 14.

While the cam follower set 20 is in engagement with the cam 14 it isnecessary to disengage the constant ratio drive through the worm 16 andworm wheel 18. In the example illustrated this is achieved by formingthe worm wheel 18 with the teeth missing, as at 24, corresponding to theposition where the cam follower engages with the cam.

The cam track 22 is raised from the surface of the cam 14 and each camfollower set 20 includes two rollers 26 which engage respective sides ofthe track 22. An alternative arrangement is shown in FIG. 3, in whichthe cam track takes the form of a groove 30 and each cam follower setconsists of a single roller 32 which runs in the groove.

The cam of FIG. 3 can be readily modified as shown in FIG. 4 to providea drive mechanism of particularly simple construction. Here, the outersurface of the cam 34 is toothed to provide a straight or globoidal wormwhich engage with the worm wheel 18. A cam follower set 36 projects fromthe center of the missingtooth portion 24 in the worm wheel 18 andcarries a single roller 38 which engages the track 30 in the worm In theembodiment shown in FIGS. 5 and 6 the cam 14 is similar to that ofFIG. 1. However, the worm 16 is replaced by a bevel gear 42 on the shaft44. A spur pinion 46 is also fixed on the shaft 44 and engages a spurgear 48 mounted on the shaft 12 and which replaces the worm wheel 18 ofFIG. 1. The spur gear 48 carries the cam followers 26 and also has a gap24 where there are no teeth, in which position the cam and cam followerare in engagement.

FIGS. 7 and 8 show a further embodiment which employs a concavegloboidal cam 50 which engages with a cam follower set 52 attached tothe spur gear 48 which is mounted on the driven shaft 12. The shaft 10also carries a spiral gear 54 which engages a spiral gear 56 on a shaft44 which also carries a spur pinion 46 for engagement with the spur gear48. Again, the spur gear 48 has a gap 24 where teeth are missing, and onrotation of the shaft from the position illustrated first the gear 48 isaccelerated to constant speed by the cam 50, whereupon the pinion 46engages the gear 48 and drive is transmitted at constant speed ratio.When the gap 24 again reaches the pinion 46 the follower 52 againengages the cam 50 to decelerate the gear 48 to rest.

The arrangements illustrated enable an indexing cycle to occupy morethan one revolution of the driving member, thus saving space and cost.Furthermore, successive indexing cycles need not employ the same numberof revolutions.

I claim:

1. A drive mechanism, comprising:

a. driving member;

a. driven member;

a cam coupled to one of said members;

a [cam follower] plurality of cam followers coupled to the other of saidmembers at diflerent angular positions for engagement with said cam whensaid members are within [a range] respective ranges of relativepositions to transmit drive from said driving member to said drivenmember; and

constant ratio gears connecting said driving and driven members whensaid members are not within said [range] ranges of relative positions.

2. A drive mechanism as claimed in claim 1, wherein said cam is shapedto provide a controlled acceleration prior to drive being effectedthrough said constant ratio gears and a controlled deceleration afterdrive from said constant ratio gears is discontinued.

3. A drive mechanism as claimed in claim 1, wherein said cam is on saiddriving member and [said] each cam follower is on said driven member,and said constant ratio gears provide a decreased velocity ratio.

4. A drive mechanism as claimed in claim 1, wherein one of said constantratio gears has teeth missing [as] at positions corresponding to [said]each range of positions where drive is transmitted through said cam andcam follower.

5. A drive mechanism as claimed in claim 1, wherein said cam is formedin one of said constant ratio gears.

6. A drive mechanism as claimed in claim 1, wherein said constant ratiogears comprise a worm driven by said driving member and a worm wheeldriving said driven member.

7. A drive mechanism as claimed in claim 1, wherein said constant ratiogears comprise a pair of spur gears one of which is driven by saiddriving member and the other of which drives said driven member.

8. A drive mechanism as claimed in claim 1, [having a plurality of camfollowers with corresponding ranges of relative positions] wherein saidconstant ratio gears comprises a pair of bevel gears one of which isdriven by said driving member and the other of which drives said drivenmember.

9. A drive mechanism as claimed in claim I, wherein each cam follower ismounted on one of said constant ratio gears.

10. A drive mechanism as claimed in claim I, wherein said constant ratiogears consist of a first gear mounted on the same shaft as the cam and asecond gear driven by said first gear and mounted on said driven member.

11. A drive mechanism as claimed in claim 1, wherein and cam is agloboidal cam.

12. A drive mechanism, comprising:

a driving member;

a driven member;

a globoidal cam coupled to one of said members;

a cam follower coupled to the other of said members for engagement withsaid cam when said members are within a respective range of relativepositions to transmit drive from said driving member to said drivenmember, the cam follower moving in a plane containing the axis ofrotation of the globoidal cam; and

constant ratio gears connecting said driving and driven members whensaid members are not within said range of relative positions.

13. A drive mechanism as claimed in claim 12, wherein said cam is shapedto provide a controlled acceleration prior to drive being efiectedthrough said constant ratio gears and a controlled deceleration afterdrive from said constant ratio gears is discontinued.

14. A drive mechanism as claimed in claim 12, wherein said cam is onsaid driving member and the cam follower is on said driven member, andsaid constant ratio gears provide a decreased velocity ratio.

15. A drive mechanism as claimed in claim 12, wherein one of saidconstant ratio gears has teeth missing at positions corresponding to therange of positions where drive is transmitted through said cam and camfollower.

16. A drive mechanism as claimed in claim 12, wherein said cam is formedin one of said constant ratio gears.

17. A drive mechanism as claimed in claim 12, wherein said constantratio gears comprise a worm driven by said driving member and a wormwheel driving said driven member.

18. A drive mechanism as claimed in claim 12, wherein said constantratio gears comprise a pair of spur gears one of which is driven by saiddriving member and the other of which drives said driven member.

19. A drive mechanism as claimed in claim 12, wherein said constantratio gears comprise a pair of bevel gears one of which is driven bysaid driving member and the other of which drives said driven member.

20. A drive mechanism as claimed in claim 12, wherein the cam followeris mounted on one of said constant ratio gears.

21. A drive mechanism as claimed in claim 12, wherein said constantratio gears consist of a first gear mounted on the same shaft as the camand a second gear driven by the first gear and mounted on the drivenmember.

References Cited The following references, cited by the Examiner, are ofrecord in the patented file of this patent or the original patent.

UNITED STATES PATENTS 3,049,017 8/1962 McDonald et al. 74-426 X LEONARDH. GERIN, Primary Examiner US Cl. X.R.

